The purpose of this project is to pursue our exploration of the immunologic interactions between host and parasite in experimental infections with taeniid metascestodes. We aim to arrive at an understanding of the mechanism of resistance to challenge infections in immune animals and the means whereby the established metacestodes in immune animals evade immunologic rejection. This phenomenon is not only fundamental to the successful propagation of taeniid parasites of man and animals in nature, but characterizes the host-parasite relationships which develop in a broad spectrum of infectious diseases and malignancies. Our principal experimental cysticercosis model system will be T. taeniaeformis in the rat. We have established that a complement- dependent IGG2a antibody mediated immunity develops in this host. We believe that destruction of challenge organisms in the immune rat occurs largely in the liver. The experimental approaches detailed in this proposal therefore focus upon: 1) the effects of purified antibody preparations on the ultrastructural and physiologic characteristics of the organism as it develops to the stage of insusceptibility; 2) the effects of purified antibody on the pathologic reaction to migrating metacestodes in the presence and absence of specifically sensitized cells. Our purpose here is to identify and characterize the cell types which participate in the destruction of the migrating organism using both in vivo and in vitro techniques; 3) completion of our characterization of the antigens released by the metacestodes in terms of their immunogenicity, function, location and production site as well as their physicochemical characteristics and role in the host-parasite relationship.